These phantoms are used to simulate the optical and/or acoustic properties of an organ and its environment. They also make it possible to simulate diseased organs containing, for example, tumors. They are manufactured in a reproducible and controlled manner.
However, most of the time these phantoms are dedicated to single-modality (monomodal) imaging, which may be optical or acoustic. However, recently, multi-modality (multimodal) imaging has experienced considerable growth in the medical diagnostic field. This is because it makes it possible to obtain both morphological and functional information. The morphological information is obtained by the use of x-rays or ultrasound. The functional information is obtained by using PET (positron emission tomography), MRI (magnetic resonance imaging) or fluorescence techniques. In particular, coupling ultrasonic imaging with fluorescence imaging seems to be particularly relevant for certain medical applications, such as mammography or diseases of the brain, prostate or testicles, since these two imaging techniques are compatible in terms of cost, size of the probes and depth of penetration. In this case, the phantom must enable both optical properties and acoustic properties to be simulated. The optical properties to be simulated are the light absorption (μa) and the light scattering (μs′) by the organ. The ultrasonic properties to be simulated are the power backscattered by the organ, which may be determined by measuring the average intensity of the signal coming from one or more sensors constituting an echographic probe. These ultrasonic parameters are also statistical parameters of the signal, such as the signal-noise ratio, or indicators determined by processing the acoustic signal such as, for example, the effective density of the scatterers present.
The literature describes phantoms for simulating the ultrasonic characteristics of living tissue. In particular, mention may be made of the following publications: de Korte, C. L., Pasterkamp, G., van der Steen, A. F. W., Woutman, H. A. and Born, N. (2000), “Characterization of Plaque Components With Intravascular Ultrasound Elastography in Human Femoral and Coronary Arteries In Vitro”, Circulation 102(6), 617-623; Ryan, L. K. and Foster, F. S. (1997) “Tissue equivalent vessel phantoms for intravascular ultrasound.” Ultrasound in Medicine and Biology 23: 261-273 and also Madsen, E. L., Berg, W A., Mendelson, E. B. and Frank, G. R., “Anthropomorphic breast phantoms for qualification of Investigators for ACRIN Protocol 6666”, Radiology, 2006 June, 239(3):869-74.
There are also publications on the simulation of optical characteristics, such as scattering and absorption. The following publications may be mentioned: Hebden, J. C., Price, B. D., Gibson, A. P., et al. “A soft deformable tissue-equivalent phantom for diffuse optical tomography”, Physics in Medicine and Biology, Volume: 51 Issue: 21 Pages: 5581-5590 and Baeten, J., Niedre, M., Dunham, J., et al., “Development of fluorescent materials for diffuse fluorescence tomography standards and phantoms”, Optics Express Volume: 15 Issue: 14 Pages: 8681-8694.
Also found are bimodal phantoms for other imaging modes. Thus, Bronskill's team describes, in the reference publication McDonald, M., Lochhead, S., Chopra, R. and Bronskill, M. J. (2004), “Multi-modality tissue-mimicking phantom for thermal therapy.” Physics in Medicine and Biology 49: 2767-2778, a phantom mimicking the ultrasonic and optical properties of living tissue. However, this phantom represents only the light absorption characteristic and not the essential scattering characteristic.